1. Field of the Invention
The present invention relates to the use of polymeric additives comprised of the reaction product of polyvinyl alcohol and hydroxybutanal as water reducing additives for cement and to cement compositions containing these additives.
2. Description of the Prior Art
Additives for cement to increase the fluidity of cement paste, mortars and concretes have been known and in use for many years. These admixtures are also known as water reducers because they allow less water to be used in a mortar or concrete without loss of slump. The performance requirements for water reducing admixtures are specified in ASTM Method C494-92, "Standard Specifications for Chemical Admixtures for Concrete."
In ASTM C494-92, a water reducing admixture is defined as an admixture that reduces the quantity of mixing water required to produce concrete of a given consistency by at least 5%.
A high range water reducing admixture, also known as a superplasticizer, reduces the quantity of mixing water required to produce concrete of a given consistency by 12% or greater. Commercial water reducing admixtures include lignin sulfonates and naphthalene sulfonate-formaldehyde condensates. More recently, new classes of flow enhancers or water reducers have been described. U.S. Pat. No. 4,814,014 describes a cement composition containing a graft co-polymer containing a polyether backbone grafted to ethylenically unsaturated monomers such as acrylic acid. U.S. Pat. No. 5,393,343 describes a cement composition containing an imidized acrylic polymer made, for example, by reacting a polyacrylic acid of 2000 molecular weight with a polyethylene polypropylene oxide polymer of 2000 molecular weight terminated at one end by a primary amine group and at the other end by a methyl group.
The compositions of the prior art have not, however, been entirely satisfactory leaving much room for improvement.